Method of false-twisting plural ends of thermoplastic yarn



June 23, 1910 B. R. FAIN 3,516,240

METHOD OF FALSE-TWISTING PLURAL ENDS OF THERMOPLASTIC YARN Filed Oct 21,1968 2 Shets-Sheet'l ATTORNEYS B. R. FAIN June 23, 1970 METHOD OFFALSE-TWISTING PLURAL ENDS OF THERMOPLASTIC YARN Filed Oct. 21, 1968 2Sheets-Sheet 2 INVENTOR. BOBBY RAY FA) N BYW 524 dig, 1! film,

ATTORNEY:

United States Patent 3,516,240 METHOD OF FALSE-TWISTING PLURAL ENDS 0FTHERMOPLASTIC YARN Bobby Ray Fain, Burlington, N.C., assignor toAlamance Industries, Inc., Burlington, N.C., a corporation of NorthCarolina Filed Oct. 21, 1968, Ser. No. 769,219 Int. Cl. D02g 1/02 U.S.Cl. 57-157 10 Claims ABSTRACT OF THE DISCLOSURE Plural ends ofthermoplastic yarn are joined together and first false-twisted in onedirection while being heatset, then subsequently false-twisted in theopposite direction with the same number of turns but withoutheatsetting, and then the yarns are separated and taken up on separatebobbins. Torsional stresses are imparted to the yarn by this process sothat periodically reversing small closely spaced substantially uniformspring-like coils are formed along the length of the yarn.

This invention relates generally to a method of simultaneouslyfalse-twisting plural ends of thermoplastic yarn to impart enhancedtorsional stresses to the yarns.

It is known to produce reversing torsional stresses in thermoplasticyarn by passing the yarn over a heated blade in what is known as anedge-crimping process. It is also known to produce reversing torsionalstresses in thermoplastic yarn by simultaneously false-twisting a pairof yarns in one direction while heat-setting the twisted together yarnsand then oppositely false-twisting the paired yarns in a secondoperation while applying a lesser number of turns and a reducedheat-setting temperature to the yarns. The yarns produced by either ofthese methods are characterized by periodically reversing small closelyspaced substantially uniform springlike coils along the length thereof.When these yarns are knit to form fine gauge fabric, such as ladieshosiery, the stitch loop interconnected prevents full development of thecoils in the yarn but a sufficient distortion of the yarn is obtained toprovide stretch and a creped appearance to the fabric.

In each of these procedures the production cost is relatively highbecause, in the edge-crimping process, it is difficult to maintain theblade in properly sharpened condition for long periods of time. In theother process,

two separate false-twisting operations must be employed.

Hosiery knit of yarns processed by the edge-crimping" method havesufficient stretch to cling to the leg but are slow to recover afterhaving been stretched to near their stretch limit, as when the fabric inthe knee area is stretched when the leg is bent.

With the foregoing in mind, it is an object of the present invention toprovide a method of false-twisting plural ends of thermoplastic yarnwhich may be carried out in a continuous and economical manner, andwhich method produces suflicient torsional stress to the yarn thatimproved stretch recovery is imparted to fine gauge fabrics, knit of theyarn, such as ladies sheer hosiery.

According to a preferred embodiment of the present invention, the joinedtogether yarns are looped about the exit pin of a false-twist spindle insuch a manner that the yarns rub across themselves while being firstfalsetwisted in one direction. In this first false-twist operation, thetwisted together yarns are heat-set in advance of the false-twistspindle. The joined yarns are subsequently false-twisted in the oppositedirection with the same number of turns but without heat-setting, andthe yarns are wrapped about the exit pin with a single 360 degree wrapduring the second false-twisting operation. The process is carried outin a continuous manner and requires only minor modifications of aconventional type false-twist machine.

Some of the objects of the invention having been stated, other objectswill appear as the description proceeds when taken in connection withthe accompanying drawings, in which- FIG. 1 is a somewhat schematicisometric view of a small section of a preferred type of false-twistapparatus for carrying out the method of the present invention;

FIG. 2 is a greatly enlarged fragmentary view of the upper end portionof the first false-twist spindle and illustrating the manner in whichthe joined together yarns are initially threaded or looped around theexit pin;

FIG. 3 is a view similar to FIG. 2 illustrating the direction in whichthe looped yarn runs across and over itself at the exit pin when thefirst false-twist spindle is rotated in a counterclockwise direction;

FIG. 3A is a View similar to FIG. 3 but illustrating the yarns beinglooped in the opposite direction when the first false-twist spindle isrotated in a clockwise direction;

FIG. 4 is a view similar to FIG. 3, but illustrating the manner in whichthe joined together yarns are wrapped about the exit pin of the secondfalse-twist spindle;

FIG. 5 is a greatly enlarged fragmentary view of one of thefalse-twisted yarns in partially relaxed condition, illustrating theflattened appearance of the yarn and the formation of the periodicallyreversing coils therein;

FIG. 6 is an elevational view of a boarded seamless stocking wherein theleg and foot portions are knit of yarn processed in accordance with themethod of the present invention; and

FIG. 7 is a greatly enlarged fragmentary portion of the knit fabric inrelaxed condition, being taken in substantially that area of the leg ofthe stocking enclosed by the dotted square 7 in FIG. 6, and illustratingthe irregular distortion of the yarn in the stitch loops to providestretch and a creped appearance to the fabric.

The present invention is particularly concerned with a method offalse-twisting plural ends of thermoplastic yarns which fall within therange of those yarns normally used in knitting ladies sheer hosiery andthe like, for example, within the range of about 7 to 70 denier. Theyarn may be a monofilament yarn, such as for example denier, andmultifilament yarns falling within the preferred range may also beutilized. For example, 15 denier yarn consisting of 3 filaments and 14denier yarn consisting of 2 filaments may also be utilized in thisprocess.

Referring to the drawings, FIG. 1 schematically illustrates one stationof the preferred type of apparatus used to false-twist the yarn inaccordance with the present method. The false-twist machine illustratedis of the type known as the Model 553 false-twist machine, manufacturedby Leesona Corporation, and only slight modification of this machine isrequired to adapt it to the present method. A pair of yarns Y and Y arewithdrawn from respective yarn supply :pirns and 21 which are suitablysupported on the lower portion of the machine. The yarns Y and Y arepreferably in the raw condi tion received from the yarn producer and maybe supplied with a special finish to provide proper lubrication.

The yarns Y and Y are drawn upwardly through respective guide wire loops22, 23 which are supported on a rod 24 and the yarns are joined togetheras they pass through a sinuous wire guide 25 which is attached to theleading flange of a support plate 26. The joined yarns pass on oppositesides of tension disc support posts 27 and then through a yarn guide 28.The joined together yarns pass downwardly and beneath a guide wire whichis fixed on a support rod 31. The yarns are then wound around a drivenlower feed roll 32 and a separator roll 33. As the yarns leave the lowerfeed roll 32, they are engaged by a small nip roll 32a to limit thedownward passage of twist. The yarns then pass upwardly through a yarnreceiving groove in a heater block 34, through a pigtail yarn guide 35,and into a false-twist spindle 36 which is rotated by a drive belt 37.

As shown in FIGS. 2 and 3, the upper end of the false-twist spindle 36is provided with a small exit pin 38 which is tapered inwardly towardthe center from each end and which is formed of a hard ceramic material,such as Al Si Mag. The diameter at the central portion of the pin 38 ispreferably small, on the order of .030 of an inch. The joined togetheryarns Y, Y are threaded around the exit pin 38 of the false-twistspindle 36 in a special manner, as shown in FIGS. 2, 3 and 3A, dependingupon the direction of rotation of the false-twist spindle 36. Thespecial threading of the yarns about the exit pin 38 will be presentlydescribed.

The joined yarns Y and Y are then directed upwardly from the exit pin 38and wound around a driven upper feed roll 40 and separator roll 41, thenWrapped with one and one-half turns around a guide roller 42, downwardlybeneath a guide roller 43 and then beneath a guide wire 44. From theguide wire 44, the yarns are threaded up through a second false-twistspindle 45 and wrapped about an exit pin 46 in the usual manner with asingle 360 degree wrap, as shown in FIG. 4. The second false-twistspindle 45 is rotated in an opposite direction from the false-twistspindle 36 or in a clockwise direction. This opposite rotation of thesecond false-twist spindle 45 tends to reduce this torque imparted tothe yarns by the first false-twist spindle 36.

From the false-twist spindle exit pin 46, the yarns pass upwardly andare wound about a driven upper feed roll 50 and a separator roll 51,pass upwardly over a guide roller 52 where the two ends of yarn Y and Yare separated and taken up on separate take-up packages. The yarn Y isled through a traversing yarn guide 53 and is wound onto a take-up tube54 to form a package 55. The take-up tube 54 is rotated by means of acork drive roll 56 which rotates against the surface of the yarn package55. The yarn Y' is led through a traversing yarn guide 60 and is woundonto a take-up tube 61 to form a package 62. The take-up tube 61 isrotated by means of a cork drive roll 63 which rotates against thesurface of the yarn package 62 and at the same speed as the upper corkdrive roll 56.

The speed of the lower feed roll 32 and the upper feed rolls 40, 50 isthe same to maintain tension on the joined yarns as they pass throughthe heater 34 and through the first and second false-twist spindles 36,45. The rotational speed of the upper feed rolls 40, 50 is adjustedrelative to the speed of the cork drive rolls 56, 63 so that theindividual yarns Y and Y are wound onto the respective take-up packages55, 62 with a 2% overfeed.

Thus, as illustrated in FIG. 1, the yarns Y and Y are Just false-twistedin one direction by the false-twist spindle 36 and the twisted yarns areheat-set as they move through the heater block 34. The yarns are thenfalse-twisted in the opposite direction by the spindle 45 without anyheat being applied to the yarns between the upper feed roll 40 andtake-up packages 55, 62. The false-twist spindles 36, 45 are rotated atthe same speed because they are both driven by the same drive belt 37,but are positioned on opposite sides thereof so that they rotate inopposite directions.

The only modification which must be made to the false-twist machine inorder to carry out the present process involves the addition of suitableguides to feed the two yarns from seperate pirns until they are joinedtogether at the guide wire 25, the addition of the guide rollers 42, 43,52 and the guide wire 44. The yarns are directed through the secondfalse-twist spindle 45 so that they do not pass through the heater blockat the next station, which is not shown but is positioned directlybeneath the false-twist spindle 45. The lower feed rolls which arepositioned beneath this adjacent heater block are not utilized inpracticing the method of the present invention. However, the productionof the machine is not reduced by use of the present method because twoyarns are processed together at this single station.

The special manner in which the joined yarns Y and Y' are threaded orwrapped about the exit pin 38 of the false-twist'spindle 36 isillustrated in FIGS. 2, 3 and 3A. In threading up the machine to beginthe operation, the yarns are drawn upwardly through the hollowfalse-twist spindle 36 by means of the usual threading wire, not shown,and behind the exit pin 38. A loop L is then formed (FIG. 2) and thefree end portions of the joined yarns Y and Y are then passed throughthe loop in a direction which is determined by the rotational directionof the spindle 36. The spindle shown in FIG. 2 is to be rotated in acounterclockwise direction so the yarn is drawn through the loop fromleft to right. When the spindle is to be rotated in the oppositedirection, the yarn is drawn through the loop in the opposite direction;i.e., from right to left, as shown in FIG. 3A.

The yarns are then drawn upwardly and wrapped around the upper feed roll40 and the separator roll 41 so that the loop L is closed, asillustrated in FIG. 3. The false-twist spindle 36 is shown in FIG. 3 asbeing rotated in a counterclockwise direction, looking downwardlythereon, and torque is imparted to the yarns in a Z direction. Thesecond false-twisting of the yarns in the opposite direction removes asubstantial portion of this torque so that the final yarn has only aslight amount of torque. However, the final yarn has sufiicient torquethat it is preferable that yarns of opposite torque be knit inalternation to balance the overall torque in the fabric. Thus, Z torqueyarns are formed by threading them about the exit pin of acounterclockwise rotating spindle in the manner illustrated in FIGS. 2and 3. Yarns having S torque are formed by threading them about the exitpin of a clockwise rotating spindle in the manner illustrated in FIG.3A.

'In either case, the joined together running yarns pass upwardly on oneside of the exit pin and then downwardly on the same side of the exitpin to form a loop in the yarn. These joined together yarns then passbeneath the exit pin and upwardly on the opposite side and through theloop as they leave the exit pin. Thus, the yarns rub across themselvesat the bite of the loop. The rubbing action of the yarns acrossthemselves at the exit pin 38 of the false-twist spindle 36 contributesto and aids in imparting latent torsional stresses to the yarn. Thisrubbing action combined with the heat-setting of the twisted togetheryarns below the false-twist spindle provides both torque and latenttorsional stresses to the yarns so that they curl or coil in aperiodically reversing direction, as illustrated in FIG. 5.

The processing of the yarn, in accordance with the present invention,results in a flattening of the yarn to form it into a ribbon-likeconfiguration or cross-section, and this flattening is believed toresult from the manner in which the yarns are tightly twisted togetherbelow the false-twist spindle 36 and while in a heated condition. Someof the flattening of'the yarns may also be attributed to the rubbingaction of the yarns at the special loop formed around the false-twistspindle exit pin 37. If the yarn of FIG. 5 were completely relaxed, itwould twist upon itself and form pigtails along the length thereof.However, the yarn is maintained under a sufficient tension during theprocess so that it is wound onto the takeup packages 55, 62 in asubstantially straight condition.

Before knitting, the yarn is preferably rewound from the take-uppackages 55, 62 and wound onto suitable knitting tubes while it ismaintained under a tension, from about 2 to .5 grams, so that any kinksin the yarn are removed and the yarn is wound in a straight condition. Asuitable lubricant is preferably added to the yarn as it is rewound ontothe knitting tube. During the knitting operation, the yarns are alsomaintained under a sufiicient tension that they cannot relax and formcurls or coils therein.

In knitting a ladies sheer seamless stocking, such as is shown at S inFIG. 6, a fine gauge yarn processed in accordance with the presentinvention is preferably knit in the leg and foot portion 70, 71 whilethe welt 72, shadow welt 73, heel pocket 74, and toe pocket 75 arepreferably knit of a heavier denier yarn. The leg and foot portions 70,71 are preferably knit with yarns which have been processed in oppositedirections so that the torque of the yarn in alternate courses is inreverse directions. Thus, the stitch loops in the odd numbered coursesC-1, C3 and (1-5 of FIG. 7 have a tendency to incline to the rightbecause they are knit of yarn having torque in one direction while thesitch loops in the even numbered courses C-2, (3-4 and C6 have atendency to incline to the left because they are knit of yarn havingtorque in an opposite direction. Thus, the overall torque in thestocking is balanced and there is no objectionable twisting of thestockings.

The stockings may be finished in the conventional manner, such as bydyeing and boarding. During the finishing of the stockings, the yarn inthe stitch loops tends to curl and coil, thereby distorting the yarn inthe manner illustrated in FIG. 7. This distortion of the yarn and stitchloops imparts a substantial amount of stretchability to the fabric andafter it is released, the fabric quickly returns to the relaxedcondition because the yarns have a strong tendency to return to thecrimped and curled condition. This elastic characteristic provides thestocking with a high degree of snap-back that is highly desirable as itreduces the problem of baggy knees; particularly in panty hose and thelike where the upper portion of the garment is supported in asubstantially fixed position around the waist of the wearer.

As an illustrative, but non-limiting example, very satisfactory hosieryhas been produced in accordance with yarn processed in accordance withthe following specific example. Single ends of denier monofilarnentnylon are extruded with a round cross-section and have a lubricatingfinish applied thereto of the type known as a type 1296-smooth,manufactured by Nopco Chemical Company. This application of lubricatingfinish to the yarn as it is extruded provides a low coeflicient offriction on the yarn and a slick finish which aids in running the twoyarns together.

The single ends of 15 denier monofilament yarn are withdrawn from thesupply bobbins 20, 21 (FIG. 1), joined together and passed upwardlythrough the falsetwist spindle 36, While the heater block is maintainedat a temperature of approximately 315 F., and the false-twist spindle 36is rotated at a sufiicient speed (about 345,000 r.p.m.) to impart 112turns per inch of false-twist to the joined together yarns. The yarnsare then directed through the second false-twist spindle 45 where areverse falsetwist is imparted to the yarns, without heat, and the yarnsare separated at the guide roller 52 and taken up on separate packages.The yarns between the lower feed roll 32 and the upper feed roll 40 aremaintained under constant tension and with zero overfeed, while theyarns between the upper feed roll 50 and the take-up packages 53, 62 arefed with a 2% overfeed so that they are relaxed to a very minor degree.

The yarns are threaded around the false-twist exit pin 38 of the spindle36 by the special looped or slip-knot configuration of FIGS. 2 and 3,which also provides an eflicient twist trap to prevent passage of thetwist from one side of the exit pin to the other. The joined togetheryarns are threaded around the exit pin 46 of the falsetwist spindle 45by the usual single wrap, as illustrated in FIG. 4. When the yarns Y andY are separated and taken up on the packages 55, 62, they each haveidentical characteristics and are very uniform throughout their length.Other pairs of identical 15 denier monofilament nylon yarns areprocessed in an identical manner, except that the yarns are threadedabout the exit pin 38 of the spindle 36 in the manner indicated in FIG.3A, and the false-twist spindle 36 is rotated in an opposite directionfrom that indicated in FIG. 1; i.e., in a clockwise direction.

When false-twisting other than 15 denier monofilarnent nylon, the rangeof turns of false-twist imparted at the false-twist spindles 36, may bevaried from about 80 to 125 turns per inch and the temperature of theheater block may be maintained within the range of about 300" to 400 F.,depending upon the speed of travel of the yarn through the heater blockand the type of yarn being processed. In the processing of multifilamentyarn, it is desirable to apply some prior twist to the individual yarnends before joining and false-twisting them in accordance with thepresent invention. This prior twist may vary from about 2 to 12 turnsper inch and is preferably about 3 turns per inch for 14/ 2 yarn. Thisprior twist tends to hold the yarns together and aids in the splittingapart of the yarns after they have been joined together and falsetwistedthrough both of the false-twisting spindles 36, 45.

As has been mentioned, the present process is more economical than anyknown method of imparting a crimpcurl to fine denier yarn, and hosieryknit of this yarn has enhanced stretchability and recoverability with apleasing appearance and hand. The enhanced elasticity and recoverabilityof the fabric is particularly desirable in panty hose because itprevents bagginess of the fabric in the knee area when the leg isstraightened after having been bent at the knee.

In the drawings and specification there have been set forth preferredembodiments of the invention and although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being defined in theclaims.

I claim:

1. A method of processing thermoplastic yarn to produce small closelyspaced substantially uniform springlike coils in each of said yarns, therotational direction of said coils periodically reversing along thelength of the yarn and providing a stretchable yarn suitable forknitting of hosiery and the like, said method comprising the continuoussteps of (a) joining together a pair of thermoplastic yarns,

(b) false-twisting the joined together yarns in one direction whileheat-setting the twisted together yarns,

(c) subsequently false-twisting the yarns a second time with afalse-twist in the opposite direction and applying the same number ofturns, but without applying any heat to the yarn during the secondfalse-twisting operation,

((1) separating the two yarns, and

(e) taking up the separated yarns on separate bobbins.

2. A method according to claim 1 wherein each yarn end is within therange of about 7 to denier.

3. A method according to claim 1 wherein the joined yarns arefalse-twisted in steps (b) and (c) within the range of about to turnsper inch.

4. A method according to claim 1 wherein each yarn end is 15 deniermonofilament and the joined yarns are false-twisted in steps (b) and (c)with about 112 turns per inch.

5. A method of processing thermoplastic yarn on a false-twist machineincluding first and second spaced apart false-twist spindles, eachspindle including an axial bore through which the yarn is adapted topass, an exit pin supported at one end of said spindle and having a yarnengaging central portion extending over the axial bore of said spindle,means for imparting rotation to said first and second spindles inopposite directions, and a heating zone positioned in advance of saidfirst false-twist spindle and through which the yarn passes prior tomoving through said first spindle, said method comprising the steps of(a) withdrawing a pair of yarns from corresponding supply sources andguiding the same in joined together relationship through said heatingzone and said first false-twist spindle,

(b) threading the yarns about said exit pin of said first false-twistspindle by passing the joined totogether yarns upwardly on one side ofsaid exit pin and downwardly on the same side of said exit pin to form alooped portion in the yarn, passing the yarn down around and beneathsaid exit pin and upwardly on the opposite side of the exit pin andthrough the looped portion whereby the yarns cross themselves at thebight of the looped portion,

(c) threading the joined yarns through said second false-twist spindleand about the exit pin by Wrapping the yarns thereabout,

(d) separating the joined together yarns,

(e) threading the separated yarns onto corresponding take-up packages,and

(f) continuously withdrawing the yarns from the supply packages andwinding them onto the corresponding take-up packages whilefalse-twisting the joined together yarns in one direction at said firstfalse-twist spindle and heat-setting the yarns, and subsequentlyfalse-twisting the yarns in the opposite direction at said secondfalse-twist spindle without applying any heat to the yarn, thefalse-twisting and heat-setting of the paired yarns and the rubbing ofthe yarns across themselves at said first false-twist spindle im partingtorque and latent torsional stresses thereto.

6. A method according to claim 5 wherein each end of yarn is within therange of about 7 to denier.

7. A method according to claim 5 wherein the joined yarns arefalse-twisted at both the first and second spindles within the range ofabout to turns per inch.

8. A method according to claim 5 including the step of rewinding theyarn from the take-up packages and onto knitting pirns while maintainingthe yarn under a tension of from about 2 to 5 grams to prevent kinkingof the yarn.

9. A method according to claim 8 including the step of applying alubricant to the yarn as it is being rewound from the take-up package tothe knitting pirn.

10. A method according to claim 5 wherein the heating zone includes aheater block maintained at about 315 F., each yarn is 15 deniermonofilament, and the joined yarns are false-twisted at both the firstand second spindles with about 112 turns per inch.

References Cited UNITED STATES PATENTS 2,952,116 9/1960 Burleson 57-1573,041,814 7/1962 Held 5734 3,423,924 1/1969 Comer et al. 57157 FOREIGNPATENTS 1,074,322 3/1954 France.

1,091,308 10/1954 France.

JOHN PETRAKES, Primary Examiner US. Cl. X.R. 5734

